The Causes of Cold Sores and How to Prevent Them

If you have tiny clusters of fluid-filled blisters around your lips, you’re most likely dealing with a cold sore.

A cold sore, also known as a fever blister, is a common condition that affects people of all ages. It’s estimated that about 90 percent of adults around the world test positive for the virus that causes a cold sore. (1)

Having a red, swollen, oozing blister on your face can be embarrassing. And to make matters worse, these blisters can return. (1) But the good news is that you can reduce the frequency of your outbreaks. This involves understanding what causes cold sores and how to prevent them.

What Are the Common Causes of a Cold Sore?

Cold sores or fever blisters are primarily caused by the herpes simplex virus (HSV) type 1, which is related to the virus that causes genital herpes (HSV-2). (2)

A cold sore can develop after you’ve been exposed to HSV-1. Some people become infected with this virus at a young age, usually after being kissed by someone with the virus. (3)

The virus enters the body through the skin and travels to the nerves where it can lie dormant. The virus doesn’t cause symptoms in everyone, so it is possible to have HSV-1 and not know it. (3)

You may develop a cold sore at some point, or you might never get a cold sore. Either way, you’re a carrier of the virus. Therefore, you can spread the virus to others even if you don’t have blisters. (1)

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The early signs of a cold sore include an itchy, tingling sensation around the mouth, cheeks, or nose. Tiny blisters appear one or two days after the first sign, and then burst and ooze after a few days.

Cold sores go away in about one to two weeks, but often return. Interestingly, sores tend to reappear in the same location. (1) Therefore, if you have had a cold sore on your lip, you may develop another one on the same spot.

Researchers don’t know why some people infected with the virus develop cold sores while others don’t. But it’s believed that certain factors can trigger an outbreak. These triggers include: (4)

Sometimes, the virus that causes genital herpes can also cause a cold sore. (1) This can happen if HSV-2 spreads to the lips or face after oral sex with someone who has genital herpes, or after kissing someone who has HSV-2 cold sores, warns Allison Arthur, MD, a board-certified dermatologist based in Orlando, Florida.

How Can You Help Prevent a Cold Sore?

The virus that causes a cold sore is highly contagious. One way to protect yourself — and others — is to avoid sharing personal items, especially during an outbreak. Personal items include food, drinks, eating utensils, clothes, towels, and even makeup. (1)

Also, avoid skin-to-skin contact during an outbreak. This includes abstaining from sexual activity until blisters heal and scab over. (1)

Even though cold sores often develop on or around the lips, the virus can also spread to other parts of your body. This might happen if you touch a cold sore and then touch another area of your body. (5)

As you wait for a cold sore to heal, make a concerted effort not to touch your sore. Understandably, you have to touch the sore to apply cold sore creams or ointments. Rather than use your finger, use a cotton swab to dab on creams. If using your finger, wash your hands with soap and water immediately after applying the medication. (5)

If your child has a cold sore, encourage them not to suck his or her thumb. Thumb-sucking could spread the virus to their hand. (1)

More on Managing Cold Sores

An outbreak is always a possibility once you’re infected with the virus that causes a cold sore. You can reduce the frequency of an outbreak by avoiding known triggers. These vary from person to person, so you’ll need to be observant to identify your individual triggers.

For example, you may experience outbreaks after strong sun exposure. If so, you can possibly prevent an outbreak by wearing sunblock or staying indoors during the heat of the day. On the other hand, if you have more outbreaks when you’re tired, improving the quality of your sleep may reduce your number of cold sores. (6)

Unfortunately, you may experience numerous outbreaks. If you have repeated cold sore outbreaks, speak with your doctor to see if you're a candidate for suppressive therapy, as recommended by Amesh A. Adalja, MD, a senior scholar at Johns Hopkins Center for Health Security based in Pittsburgh.

If so, your doctor will prescribe an antiviral that you can take daily, such as: (7)

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A Final Word on Cold Sore Causes and Prevention

Even a single cold sore may feel like one too many. But the good news is that cold sores don’t have to take over your face. Understanding and avoiding your triggers may reduce your number of outbreaks. And if not, don’t hesitate to talk to your doctor about medications to control symptoms.

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